With the increasing demand of users for rich visual interaction, a large-size screen (large screen for short below) has found increasingly wide use. The large-size screen herein may be a display device that can display different content in different areas, and may also be a display device that can simultaneously display different content for different receivers. The arrangement of both a large screen arranged fixedly and a movable large screen in a scenario such as a home, an office, and a public place can meet watching demand at any time and any place of users. With the development of large screen technologies, 2D display, 3D display, interaction performance, and the like, on a large screen are enhanced. Particularly, in terms of user interaction, a large screen can achieve interaction for users possessing various mobile devices (comprising a mobile phone, a portable notebook, a wearable device, and the like). When a screen of a mobile device of a user cannot provide optimal experience for the user, or the mobile device of the user cannot provide visual interaction for the user, the user may project content that the user is to watch on a large screen arranged nearby, so as to implement sharing between the mobile device and the large screen, thereby meeting the demand of the user for visual interaction. However, security and privacy concerns of large-screen sharing (especially a large screen in a public place) become issues that constrain the rapid development and wide use of large screen technologies and require an urgent solution.